1. Field of the Invention
This invention relates to devices which are caused to traverse the interior of a pipeline and, in the course of traversal, are used for performing a desired operation upon the internal wall of a pipeline, such as painting, cleaning, scraping or the like. Particularly, the invention relates to structures associated with pipeline pigs adapted to be propelled through a pipeline, which structures bear against the internal wall of the pipeline during the course of travel of the pig and effect a desired treatment of such internal wall.
2. Brief Description of the Prior Art
As is well known in the gas and oil industry, and particularly among pipeline technologists and personnel, the extremely corrosive and abrasive wear to which the internal surfaces of pipelines used for transporting various types of hydrocarbons, brine, water or other chemical materials, are subjected, requires that such pipelines be frequently cleaned or treated so that replacement of sections of the pipeline due to excessive weakening can be deferred. This type of maintenance of the internal surfaces of the pipeline is carried out in various ways, but often involves the mounting of selected types of abrading or treating devices on a pipeline pig for movement with the pig through the pipeline. Such pigs are propelled through the pipeline by a mechanical pulling device, or more often, by fluid pressure exerted on the trailing end of the pig to propel it in a longitudinal direction through the pipeline.
Treatments of internal surfaces of pipelines which entail the application thereto of a treating fluid, such as paint, corrosion inhibitors, drying agents or a solvent, frequently achieve less than optimum results due to the fact that the paint or other treating fluid is not evenly applied. In some instances, gaps or holidays are left on the internal surface of the pipeline at locations where the treating elements used to apply the paint or other treating fluid have not made contact with the internal surface of the pipeline. Such failure of the treating elements to completely apply the treating material to the internal surface of the pipeline results in an aggravation of the problem of localized pitting or wear, and in some cases substantially decreases the service life of the pipeline due to the concentration of corrosive or abrasive forces at the untreated locale during continued use of the pipeline.